The present invention relates to ion exchange resins, and in particular, to a process for preparing such resins.
Copolymer particles or beads prepared from polymerized monomers of mono- and poly-ethylenically unsaturated monomers are converted to anion exchange resins or beads using various techniques. For example, weak base resins can be prepared by haloalkylating poly(vinyl aromatic)copolymer beads and subsequently functionalizing the haloalkylated copolymers.
Methods for haloalkylating crosslinked addition copolymers, as well as haloalkylating agents included in such methods are disclosed, for example, in U.S. Pat. Nos. 2,642,417; 2,960,480; 2,597,492; 2,597,493; 3,311,602 and 2,616,817 and Ion Exchange by F. Helfferich, published in 1962 by McGraw Hill Book Co., New York, all of which are incorporated herein by reference. Typically, the haloalkylating reaction involves swelling the crosslinked addition copolymer (e.g., crosslinked polystyrene) with a haloalkylating agent (e.g., bromomethylmethyl ether, chloromethylmethyl ether, or a mixture of formaldehyde and hydrochloric acid) and reacting the mixture in the presence of a Friedel-Crafts catalyst such as zinc chloride, iron chloride and aluminum chloride.
Generally, ion exchange beads are prepared from the haloalkylated bead by contacting said bead with a compound capable of displacing the halogen of the haloalkyl group and which, upon reaction, forms an active ion exchange group. Such compounds and methods for preparing ion exchange resns therefrom (i.e., weak base resins and strong base resins) are well known in the art and U.S. Pat. Nos. 2,632,000; 2,616,877; 2,642,417; 2,632,001; 2,992,544 (all of which are hereby incorporated by reference) and F. Helfferich supra are illustrative thereof. Typically, a weak base resin is prepared by contacting the haloalkylated copolymer with ammonia, a primary amine or a secondary amine, or polyamines such as ethylene diamine, propylene diamine, and the like. Representative primary and secondary amines include the methyl amine, ethyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine and the like, as well as various polyamines. Strong base ion exchange resins are prepared using tertiary amines such as trimethyl amine, triethyl amine, tributyl amine, dimethylisopropanol amine, ethylmethylpropyl amine, dimethylamino ethanol, or the like as aminating agents.
Amination generally comprises heating a mixture of the haloalkylated copolymer beads and at least a stoichiometric amount of the aminating agent, (i.e., ammonia or the amine) to a temperature sufficient to displace the halogen atom attached to the carbon atom .alpha. to the aromatic nucleus of the polymer with aminating agent. A reaction medium such as water, ethanol, methanol, methylene chloride, ethylene dichloride, dimethoxymethylene, or combinations thereof is optionally, but advantageously employed. Conventionally, amination is carried out at conditions such that anion exchange sites are uniformly dispersed throughout the entire bead.
Unfortunately, known processes for preparing anion exchange resins do not efficiently and effectively provide as high capacity resins as would be desirable. In view of this deficiency, it would be highly advantageous to provide an improvement in the process for preparing anion exchange resins, and the product prepared therefrom having a high anion capacity and particularly a high weak base capacity.